Semiconductor device including a nitride layer

ABSTRACT

A semiconductor device, comprising a nitride semiconductor layer, a switching element, and a driving transistor; the switching element comprises: a first portion of a first electrode formed on the nitride semiconductor layer; a second electrode formed on the nitride semiconductor layer; and a first control electrode formed on the nitride semiconductor layer and located between the first portion of the first electrode and the second electrode; the driving transistor comprises: a second portion of the first electrode formed on the nitride semiconductor layer and connecting the first portions of the adjacent first electrodes to each other; a third electrode formed on the nitride semiconductor layer and transmitting a signal to the first control electrode; and a second control electrode formed on the nitride semiconductor layer and located between the second portion of the first electrode and the third electrode. Therefore, when the switching element is turned off, it can be kept in an off state even if a drain voltage applied to the switching element is subjected to a variation or the like.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a National Stage of International Application No.PCT/JP2017/033611, filed on Sep. 15, 2017.

TECHNICAL FIELD

The present invention relates to a semiconductor device comprising aswitching element and a driving transistor.

BACKGROUND OF THE INVENTION

The Group III-V nitride compound semiconductor represented by thegallium nitride (GaN), i.e., the so-called nitride semiconductor hasattracted attention. The nitride semiconductor is a compoundsemiconductor having a general formula represented asIn_(x)Ga_(y)Al_(1−x−y)N (0≤x≤1, 0≤y≤1, x+y≤1) and composed of aluminum(Al), gallium (Ga) and indium (In) as group III elements and nitrogen(N) as a group V element. The nitride semiconductor can form variousmixed crystals and can easily form a hetero-junction interface. Thehetero junction of the nitride semiconductor has the followingcharacteristics: a high-concentration two-dimensional electron gas layeris generated at the junction interface due to a spontaneous polarizationand/or a piezoelectric polarization even under an undoped state. A FieldEffect Transistor (FET) employing the high-concentration two-dimensionalelectron gas layer as carriers has attracted attention as a switchingelement for high frequency and high power.

A driving transistor is required in the switching element, and it mayconsider a case where the driving transistor is provided as anindependent package and a case where the switching element and thedriving transistor are provided as a same package. In the latter case,patent document 1 and the like disclose an example in which a drivingtransistor is formed of a nitride semiconductor, and a switchingtransistor and the driving transistor are formed on a same substrate. Inthe above structure, the semiconductor device can switch at a high speedeven in cases where a gate signal is not at a high speed, an outputimpedance of a gate driving circuit is high, and an influence of awiring inductance is worried.

In such a semiconductor device, in a case where an excessive currentflows through a power line of the semiconductor device, when theconnections of wiring, wires, etc. between a source electrode of theswitching element and a source electrode of the driving transistor arelengthened, sometimes a parasitic impedance between the source electrodeof the switching element and the source electrode of the drivingtransistor is increased, and the switching element performs amisoperation or oscillation.

The source electrode of the switching element is further connected to asource terminal of the semiconductor device. Here, by causing aconnection portion between the source electrode of the drivingtransistor and the source electrode of the switching element to be asclose as possible to a side of the source electrode of the switchingelement rather than to a side of the source terminal of thesemiconductor device, it is possible to divide a power line which allowsa main current to flow through the switching element, and a signal linewhich allows a signal current to flow through an inter-gate-source loopof the switching element. As a result, potential variations in apotential of a source portion of the switching element and a potentialof a source portion of the driving transistor can be suppressed, so asto suppress a misoperation or an oscillation of the switching element.

DOCUMENTS OF THE PRIOR ARTS Patent Document(s)

Patent Document 1: Japanese Patent Laid-Open No. 2012-222393

SUMMARY OF THE INVENTION The Problem to be Solved by the PresentInvention

However, a threshold value of a switching element formed by a nitridesemiconductor is low. Thus, in an off state of such a switching element,a difference between an output voltage of a driving transistor and athreshold voltage of the switching element becomes smaller. When theimpedance generated in a loop connecting the switching element and thedriving transistor increases, the off state of the switching elementcannot be maintained due to a variation in a drain voltage of theswitching element or the like. Furthermore, sometimes the switchingelement performs a misoperation or oscillation.

Therefore, the present invention is proposed in view of the aboveproblem, and an object is to provide a semiconductor device capable ofsuppressing a value of impedance generated in a loop connecting aswitching element and a driving transistor.

Means for Solving the Problem

In order to achieve the above object, a semiconductor device of thepresent invention comprises a nitride semiconductor layer, a switchingelement, and a driving transistor; the switching element comprises: afirst portion of a first electrode formed on the nitride semiconductorlayer; a second electrode formed on the nitride semiconductor layer; anda first control electrode formed on the nitride semiconductor layer andlocated between the first portion of the first electrode and the secondelectrode; the driving transistor comprises: a second portion of thefirst electrode formed on the nitride semiconductor layer and connectingthe first portions of the adjacent first electrodes to each other; athird electrode formed on the nitride semiconductor layer andtransmitting a signal to the first control electrode; and a secondcontrol electrode formed on the nitride semiconductor layer and locatedbetween the second portion of the first electrode and the thirdelectrode.

Effects of the Present Invention

As described above, the semiconductor device according to the presentinvention can suppress the value of impedance generated in the loopconnecting the switching element and the driving transistor.

Therefore, in the off state of the switching element, the misoperationor oscillation of the switching element can be suppressed.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic cross-sectional view illustrating a semiconductordevice according to a first embodiment.

FIG. 2 is a schematic circuit diagram illustrating a semiconductordevice according to a first embodiment.

FIG. 3 is a schematic top view illustrating a semiconductor deviceaccording to a first embodiment.

FIG. 4 is a top view of a semiconductor device according to a secondembodiment.

FIG. 5 is a top view of a semiconductor device according to a thirdembodiment.

FIG. 6 is a circuit diagram of a semiconductor device according to athird embodiment.

FIG. 7 illustrates a turned-on waveform and a turned-off waveform of asemiconductor device according to a third embodiment.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Hereinafter, the present invention will be described in detail withreference to the drawings as examples of the embodiments, but thepresent invention is not limited thereto. In addition, a ‘connection’described herein further comprises a connection with a load, such as aresistor, an inductor, etc., and any other element, such as a diode⋅ atransistor, etc., interposed therebetween, unless otherwise specified inthe claims of the present invention.

Firstly, a semiconductor device according to a first embodiment will bedescribed with reference to FIG. 1. In addition, the cross-sectionalview of FIG. 1 is taken along A-A in the top view of FIG. 3.

FIG. 1 is a schematic cross-sectional view illustrating a semiconductordevice 10 according to a first embodiment. The semiconductor device 10of FIG. 1 comprises a substrate 14 made of silicon or silicon carbide; abuffer layer 15 formed on the substrate 14 and made of a nitridesemiconductor; a channel layer 16 and a barrier layer 17 that are madeof nitride semiconductors; and a two-dimensional electron gas layer 18generated in a planar expansion manner near an interface with thechannel layer 16 and the barrier layer 17. In the semiconductor device10 of FIG. 1, a gallium nitride (GaN) layer 12 is provided on thebarrier layer 17, but the gallium nitride (GaN) layer 12 also may not beformed.

The buffer layer 15 may also be a structure in which aluminum galliumnitride (AlGaN) or aluminum nitride (AlN) is provided on the substrate14. In addition, the buffer layer 15 may be a multilayer structure inwhich a first layer made of aluminum nitride (AlN) and a second layermade of aluminum gallium nitride (AlGaN) or gallium nitride (GaN) arerepeatedly formed on the substrate 14. In addition, the buffer layer 15may also be a structure having a concentration gradient in which acomposition ratio of aluminum on the substrate 14 decreases stepwise orgradually as approaching the channel layer 16 from a side of thesubstrate 14.

The channel layer 16 is made of gallium nitride (GaN), and as a nitridesemiconductor having a composition different from that of the channellayer 16, the barrier layer 17 is for example made of aluminum galliumnitride (AlxGa1−xN; wherein x is great than 0 and less than 1). A spacerlayer made of aluminum nitride (AlN) is interposed between the channellayer 16 and the barrier layer 17. In this case, the semiconductordevice 10 has the two-dimensional electron gas layer 18 generated in aplanar expansion manner on a side of the channel layer 16 near aninterface between the spacer layer and the channel layer 16.

A switching element 100 and a driving transistor 200 are formed in thesemiconductor device 10. Between the switching element 100 and thedriving transistor 200, there is an element separation structure 19composed of an ion implantation region or a groove. The elementseparation structure 19 reaches the channel layer 16 more deeply from anupper surface of the barrier layer 17 than the two-dimensional electrongas layer 18. By providing the element separation structure 19, thetwo-dimensional electron gas layer 18 in the region of the switchingelement 100 is separated from the two-dimensional electron gas layer 18in the region of the driving transistor 200. In addition, in the elementseparation structure 19, instead of forming a groove, a region in whichions are implanted into the barrier layer 17 without generating thetwo-dimensional electron gas layer 18 may be formed. In addition, theelement separation structure 19 also may not be provided.

The switching element 100 comprises a drain electrode (second electrode)22 provided on the barrier layer 17 and electrically connected to thetwo-dimensional electron gas layer 18. In addition, as illustrated inFIG. 3, when the semiconductor device is viewed from above, theswitching element 100 is provided with a source electrode (first portionof a first electrode) 21 so as to surround the drain electrode (secondelectrode) 22. The source electrode (first portion of the firstelectrode) 21 is provided on the barrier layer 17 and electricallyconnected to the two-dimensional electron gas layer 18. In addition, afirst control electrode 31 is provided on the barrier layer 17 betweenthe drain electrode (second electrode) 22 and the source electrode 21.

The driving transistor 200 comprises a source electrode (second portionof the first electrode) 23 provided on the barrier layer 17 andelectrically connected to the two-dimensional electron gas layer 18.

As illustrated in FIG. 3, when the semiconductor device 10 is viewedfrom above, the source electrode 23 is formed so as to connect endportions of the adjacent source electrodes 21 in a long-side directionto each other. In addition, the source electrode 23 is formed so as toconnect left end portions of the adjacent source electrodes 21 in thelong-side direction to each other, and a long-side direction (extendingdirection) of the source electrode 23 is a direction crossing, andpreferably perpendicular to, the long-side direction (extendingdirection) of the source electrode 21. Therefore, as illustrated in FIG.3, when the semiconductor device 10 is viewed from above, a length froma portion of the source electrode 21, which is a region in which theswitching element surrounded by a dotted line functions, to a portion ofthe source electrode 23, which is a region in which the drivingtransistor 200 surrounded by a dotted line functions, or a sum thereofbecomes shorter.

In addition, the driving transistor 200 has a drain electrode (thirdelectrode) 24 provided on the barrier layer 17 and electricallyconnected to the two-dimensional electron gas layer 18, and has a secondcontrol electrode 32 provided on the barrier layer 17 between the sourceelectrode 23 and the drain electrode 24. As illustrated in FIG. 3, whenthe semiconductor device 10 is viewed from above, the source electrode23 is configured more closely to the side of the switching element thanthe drain electrode 24. Furthermore, a long-side direction (extendingdirection) of the drain electrode 24 is formed to be extended in adirection perpendicular to a long-side direction (extending direction)of the first control electrode 31.

Therefore, an in-plane deviation of the parasitic impedance generatedbetween the drain electrode 24 and the first control electrode 31 can besuppressed, and the parasitic impedance generated between the drainelectrode 24 and the first control electrode 31 can be reduced.

In addition, as illustrated in FIG. 3, when the semiconductor device 10is viewed from above, the adjacent first control electrodes 31 areconnected to each other so as to surround the drain electrode 22.

In addition, as illustrated in FIG. 3, when the semiconductor device 10is viewed from above, the first control electrode 31 is configuredseparately from the second control electrode 32 and the source electrode23 in a portion of the first control electrode 31 crossing the secondcontrol electrode 32 and the source electrode 23.

In addition, in the semiconductor device 10 of FIG. 3, the adjacentdrain electrodes 22 are connected to each other through wiring notillustrated. In addition, in the semiconductor device 10 of FIG. 3, anoutput terminal (drain terminal) of the semiconductor device 10 notillustrated is connected to the drain electrode 22 of the switchingelement 100, an input terminal INL of the semiconductor device 10 notillustrated is connected to the gate electrode 32 of the drivingtransistor 200, and a source terminal S of the semiconductor device 10is connected to the source electrode 21 of the switching element 100 ata connection point F as close as possible to the source electrode 21 ofthe switching element 100.

The circuit diagram of FIG. 2 illustrates a circuit structure of such asemiconductor device 10. In the circuit diagram of FIG. 2, D denotes anoutput terminal (drain terminal) of the semiconductor device 10, INLdenotes an input terminal of the semiconductor device 10, and S denotesa source terminal of the semiconductor device 10. The drain terminal Dof the semiconductor device 10 is connected to the drain electrode 22 ofthe switching element 100, and the gate electrode (first controlelectrode) 31 of the switching element 100 is connected to the drainelectrode 24 of the driving transistor 200. The gate electrode (secondcontrol electrode) 32 of the driving transistor 200 is connected to theinput terminal INL of the semiconductor device 10, and the sourceelectrode 23 of the driving transistor 200 is connected to the sourceelectrode 21 of the switching element 100. Here, a parasitic inductanceLSF denotes a parasitic inductance generated between the sourceelectrode 21 of the switching element 100 and the source terminal S ofthe semiconductor device 10 by providing the connection point F on theside of the electrode 21, a parasitic inductance LSS1 denotes aparasitic inductance generated between the gate electrode 31 of theswitching element 100 and the drain electrode 24 of the drivingtransistor 200, and a parasitic inductance LSS2 denotes a parasiticinductance generated between the source electrode 21 of the switchingelement 100 and the source electrode 23 of the driving transistor 200.As illustrated in FIG. 3, in the semiconductor device 10, since a lengthfrom a source electrode portion of the source electrode 21, which is aregion in which the switching element 100 is surrounded by a dottedline, to a source electrode portion of the source electrode 23, which isa region in which the driving transistor 200 is surrounded by a dottedline, is short, the parasitic inductance LSS2 can be reduced. Inaddition, as illustrated in FIG. 3, in the semiconductor device 10, adirection perpendicular to an extending direction of the first controlelectrode 31 becomes an extending direction of the drain electrode 24 ofthe driving transistor 200, and each of the first control electrodes 31is connected to the drain electrode 24, so that the parasitic inductanceLSS1 generated between the drain electrode 24 and the first controlelectrode 31 can be reduced.

In addition, the connection between the source terminal S of thesemiconductor device 10 and the source electrode 21 of the switchingelement 100 is made to be close to the side of the source electrode 21of the switching element 100, rather than to the side of the sourceelectrode 23 of the driving transistor 200, so as to divide a power linewhich allows a main current to flow through the switching element 100,and a signal line which allows a signal current to flow through aninter-gate-source loop of the switching element 100, thereby suppressingpotential variations in a potential of the source electrode 21 of theswitching element 100 and a potential of the source electrode 23 of thedriving transistor 200, and then suppressing a misoperation oroscillation of the switching element 100.

In the circuit diagram of FIG. 2, the drain electrode 24 of the drivingtransistor 200 outputs High or Low according to a control signalinputted to the input terminal INL, and the output is inputted to thefirst control electrode 31 of the switching element 100, so that theswitching element 100 performs a switching operation. In the off stateof the switching element 100, the output voltage of the drivingtransistor 200 becomes zero volt (0V). Here, when the switching element100 is composed of a nitride semiconductor, the switching element 100can perform high-speed switching as compared with a switching elementmade of other semiconductor material. However, the threshold voltage(Vth) of the switching element 100 composed of the nitride semiconductoris low. As a result, a difference between the threshold voltage of theswitching element 100 and the output voltage of the driving transistor200 in the off state of the switching element 100 becomes smaller. In asemiconductor device having a switching element composed of such anitride semiconductor, in a case where a large impedance is generated ina loop connecting the switching element and the driving transistor, asin the conventional semiconductor device, the off state of the switchingelement cannot be kept due to the variation in the drain voltage appliedto the switching element 100, etc., and sometimes the switching elementperforms a misoperation or oscillation.

However, in the semiconductor device 10, since the source electrode 23is configured to connect the adjacent source electrodes 21 to eachother, the length from the source electrode 23 to the source electrode21 becomes shorter, which can reduce the parasitic inductance LSS2.Thus, the off state of the switching element can be maintained, and themisoperation or oscillation of the switching element can be suppressed.Furthermore, by connecting the source terminal S of the semiconductordevice 10 more closely to the side of the source electrode 21 than thesource electrode 23, it is possible to divide a power line which allowsa main current to flow through the switching element, and a signal linewhich allows a signal current to flow through an inter-gate-source loopof the switching element, thereby suppressing the misoperation oroscillation of the switching element.

In addition, the source electrode 23 also serves as a connection wiringfor the adjacent source electrodes 21, so as to reduce a chip area ofthe semiconductor device 10.

In addition, each of the first control electrodes 31 is connected to thedrain electrode 22 of the driving transistor 200 for example via avia-hole and wiring, so that the impedance (gate impedance of theswitching element 100) from the drain electrode 22 to each of the firstcontrol electrodes 31 becomes more uniform for the switching element100, and the misoperation of the semiconductor device 10 can besuppressed

In addition, as illustrated in FIG. 3, when the semiconductor device 10is viewed from above, the driving transistor 200 is provided on a leftside of the switching element 100. However, the adjacent sourceelectrode 21 may also be connected to an end portion on a right side ofthe long-side direction of the source electrode 21 via the sourceelectrode 23, and the driving transistor 200 may be provided on a rightside of the switching element 100. In addition, as illustrated in FIG.3, when the semiconductor device 10 is viewed from above, the adjacentsource electrodes 21 may also be connected to both ends of the sourceelectrodes 21 in the long-side direction via the source electrode 23,and the driving transistor 200 may be provided on both sides of theswitching element 100.

Next, a semiconductor device 10 a according to a second embodiment willbe described with reference to FIG. 4. FIG. 4 is a top view illustratingthe semiconductor device 10 a according to the second embodiment. Thesemiconductor device 10 a of FIG. 4 has substantially the same structureas the semiconductor device 10 according to the first embodimentillustrated in FIG. 1, and the difference lies in that in the drivingtransistor 200, the second control electrode 32, the source electrode231, the second control electrode 32, and the drain electrode 241 arerepeated as a unit one or more times on a side opposite to the switchingelement 100 with respect to the electrode 24, and the second controlelectrode 32 and the source electrode 231 are configured at the end ofthe repetition. Here, in the semiconductor device 10 a of FIG. 4, thenumber of repetitions of the unit is 1. The second control electrode 32,the source electrode 231 and the drain electrode 241 are provided on thebarrier layer 17 and are electrically connected to the two-dimensionalelectron gas layer 18.

In addition, in the semiconductor device of FIG. 4, through the wiringsnot illustrated, the adjacent source electrodes 231 are connected toeach other, the adjacent second control electrodes 32 are connected toeach other, the adjacent drain electrodes 241 are connected to eachother, the source electrodes 23 and 231 are connected to each other, andthe drain electrodes 241 and 24 are connected to each other. In thesemiconductor device 10 a according to the second embodiment, an effectthe same as that of the semiconductor device 10 according to the firstembodiment can also be achieved.

Next, a semiconductor device 10 b according to a third embodiment willbe described with reference to FIG. 5. FIG. 5 is a top view illustratingthe semiconductor device 10 b according to the third embodiment, FIG. 6is a circuit diagram illustrating the semiconductor device 10 baccording to the third embodiment, and FIG. 7 illustrates a turned-onwaveform and a turned-off waveform of the semiconductor device 10 baccording to the third embodiment.

The semiconductor device 10 b according to the third embodiment isdifferent from the semiconductor device 10 a according to the secondembodiment in that the driving transistor 300 is provided. Asillustrated in FIG. 5, when the semiconductor device 10 b is viewed fromabove, the driving transistor 200 is provided on a left side of theswitching element 100, and the driving transistor 300 is provided on aright side of the switching element 100 (a side opposite to the drivingtransistor 200). The driving transistor 300 comprises a source electrode(fifth electrode) 25 and a drain electrode (sixth electrode) 26 providedon the barrier layer 17 and electrically connected to thetwo-dimensional electron gas layer 18. In addition, the drivingtransistor 300 comprises a third control electrode 33 provided on thebarrier layer 17 between the source electrode (fifth electrode) 25 andthe drain electrode 26.

As illustrated in FIG. 5, when the semiconductor device 10 b is viewedfrom above, the source electrode 25 of the driving transistor 300 isprovided on the side of the switching element 100, and the third controlelectrode 33, the drain electrode 26, the third control electrode 33,and the source electrode 25 are repeated as a unit one or more times ona side opposite to the switching element 100. In FIG. 5, the unit isrepeated twice. In addition, in the semiconductor device of FIG. 5,through the wirings not illustrated, the adjacent drain electrodes 22are connected to each other, the adjacent source electrodes 231 areconnected to each other, the adjacent second control electrodes 32 areconnected to each other, the adjacent drain electrodes 241 are connectedto each other, the source electrodes 23 and 231 are connected to eachother, the drain electrodes 241 and 24 are connected to each other, theadjacent source electrodes 25 are connected to each other, the adjacentsecond control electrodes 32 are connected to each other, and theadjacent drain electrodes 241 are connected to each other.

In the semiconductor device 10 b according to the third embodiment, aneffect the same as that of the semiconductor device 10 according to thefirst embodiment can also be achieved.

In addition, as illustrated in FIG. 5, when the semiconductor device 10b according to the third embodiment is viewed from above, an end portionon a left side of each of the first control electrodes 31 is connectedto the drain electrode 22 of the driving transistor 200 closest to theside of the switching element, and an end portion on a right side ofeach of the first control electrodes 31 is connected to the sourceelectrode 25 of the driving transistor 300 closest to the side of theswitching element. The source electrode 25 is formed so as to connectend portions of the adjacent first control electrodes 31 in thelong-side direction (extending direction) to each other. In addition,the long-side direction (extending direction) of the source electrode 25becomes a direction perpendicular to the long-side direction (extendingdirection) of the first control electrode 31. In addition, since thelong-side direction of the first control electrode 31 is substantiallyparallel to the long-side direction of the source electrode 21, thelong-side direction (extending direction) of the source electrode 25becomes a direction perpendicular to the long-side direction (extendingdirection) of the source electrode 21. Therefore, the length from thesource electrode 25 to the first control electrode 31 also becomesshorter, and a connection portion K among the source electrode 25, thefirst control electrode 31, and the drain electrode 24 is closer to theside of the first control electrode 31 as compared with the side of thedrain electrode 24 and the side of the source electrode 25. Thus, asillustrated in the circuit diagram of the semiconductor device 10 b inFIG. 6, parasitic inductances LSS2 and LSS3 up to the source electrode25 can be reduced. As a result, the semiconductor device 10 b cansuppress potential variations in the potential of the first controlelectrode 31 of the switching element 100 and the potential of thesource electrode 25 of the driving transistor 300. In addition, theswitching element can be maintained in the off state by reducing theparasitic inductance LSS2, thereby suppressing the misoperation andoscillation of the switching element.

FIG. 7 illustrates a turned-on waveform and a turned-off waveform of thesemiconductor device in FIG. 5. In the semiconductor device according tothe third embodiment, an effect the same as that of the semiconductordevice according to the first embodiment can be achieved.

In addition, the present invention is not limited to the aboveembodiments which are just examples, and any manner is included in thetechnical scope of the present invention, as long as it hassubstantively the same structure and achieves the same effect as thetechnical idea described in the claims of the present invention. Forexample, the present invention also includes a structure in which acontact layer composed of a nitride semiconductor containing a largeamount of N-type impurities is provided between the barrier layer 17 andthe drain electrode and/or the source electrode.

REFERENCE SIGNS

-   -   10, 10 a, 10 b . . . semiconductor device    -   14 . . . substrate    -   15 . . . buffer layer    -   16 . . . channel layer    -   17 . . . barrier layer    -   18 . . . two-dimensional electron gas layer    -   19 . . . element separation structure    -   21 . . . source electrode (first portion of first electrode)    -   22 . . . drain electrode (second electrode)    -   23 . . . source electrode (second portion of first electrode)    -   24 . . . drain electrode (third electrode)    -   31 . . . gate electrode (first control electrode)    -   32 . . . gate electrode (second control electrode)    -   100 . . . switching element    -   200 . . . driving transistor

The invention claimed is:
 1. A semiconductor device, comprising anitride semiconductor layer, a switching element, and a drivingtransistor, the switching element comprises: a first portion of a firstelectrode formed on the nitride semiconductor layer; a second electrodeformed on the nitride semiconductor layer; and a first control electrodeformed on the nitride semiconductor layer and located between the firstportion of the first electrode and the second electrode, the drivingtransistor comprises: a second portion of the first electrode formed onthe nitride semiconductor layer and connected to first portions of firstelectrodes, which are adjacent to each other; a third electrode formedon the nitride semiconductor layer and transmitting a signal to thefirst control electrode; and a second control electrode formed on thenitride semiconductor layer and located between the second portion ofthe first electrode and the third electrode.
 2. The semiconductor deviceaccording to claim 1, wherein, the first control electrode is connectedto the third electrode.
 3. The semiconductor device according to claim1, wherein, the semiconductor device is formed such that a directionperpendicular to a long-side direction of the first portion of the firstelectrode becomes a long-side direction of the second portion of thefirst electrode.
 4. The semiconductor device according to claim 2,wherein, the semiconductor device is formed such that a directionperpendicular to a long-side direction of the first portion of the firstelectrode becomes a long-side direction of the second portion of thefirst electrode.
 5. The semiconductor device according to claim 1,wherein, a plurality of fourth electrodes, the second control electrodesand the third electrodes are repeatedly configured on the nitridesemiconductor layer, the fourth electrode is electrically connected tothe second portion of the first electrode, the fourth electrode isprovided on a side opposite to the switching element with respect to thesecond portion of the first electrode.
 6. The semiconductor deviceaccording to claim 2, wherein, a plurality of fourth electrodes, thesecond control electrodes and the third electrodes are repeatedlyconfigured on the nitride semiconductor layer, the fourth electrode iselectrically connected to the second portion of the first electrode, thefourth electrode is provided on a side opposite to the switching elementwith respect to the second portion of the first electrode.
 7. Thesemiconductor device according to claim 1, wherein, the drivingtransistor is a first driving transistor, the semiconductor device has asecond driving transistor, with the switching element interposed betweenthe second driving transistor and the first driving transistor, thesecond driving transistor has a fifth electrode formed on the nitridesemiconductor layer; a sixth electrode formed on the nitridesemiconductor layer; and a third control electrode formed on the nitridesemiconductor layer and located between the fifth electrode and thesixth electrode, the sixth electrode is connected to the first controlelectrode.
 8. The semiconductor device according to claim 2, wherein,the driving transistor is a first driving transistor, the semiconductordevice has a second driving transistor, with the switching elementinterposed between the second driving transistor and the first drivingtransistor, the second driving transistor has a fifth electrode formedon the nitride semiconductor layer; a sixth electrode formed on thenitride semiconductor layer; and a third control electrode formed on thenitride semiconductor layer and located between the fifth electrode andthe sixth electrode, the sixth electrode is connected to the firstcontrol electrode.